1. Field of the Invention
The invention is based on a method and apparatus for aftertreatment of exhaust gases of an internal combustion engine.
2. Description of the Prior Art
DE 199 46 902 A1 has disclosed the introduction of a urea/water solution into the exhaust train downstream of an engine to remove nitrogen from the exhaust and the provision of a return line from a supply pump back to a urea tank, which line serves to reduce an excess pressure that may potentially be present in the urea line and, for example, to bleed air from the urea line; but especially in freeze-critical situations, particularly at times other than when the reducing agent is being metered into the exhaust train, no continuous heat exchange is provided between the urea/water solution and freeze-endangered regions of the exhaust aftertreatment apparatus.
In addition, DE 102 54 981 A1 has disclosed using compressed air to remove reducing agent still contained in reducing agent-conveying lines after the metering.